Present electrophotographic copiers and printers are replete with paper or sheet transporting equipment which, despite the best engineering, occasionally jam. Modern day copiers, for example, have substantial software devoted toward detecting and notifying the operator that there is a jam, its location, and how to clear it. Typically, such jams are cleared by raising not only the top of the copier but the transport mechanism itself, which mechanism is pivotable to a raised position thereby separating its drive train.
Some disengageable couplings for such a drive train presently involve simple channel and projection mating surfaces. One of the driving shafts rotates until the channel and projection mate engaging the coupling. 100% alignment of the two shafts is virtually impossible, especially if jams are common and the copiers heavily used. The simple channel and projection (or pin and slot) coupling can refuse to couple with too much misalignment, or, once coupled, it can cause wobble distributed between the two shafts and generally abrupt uneven movement.
A flexible engageable coupling allows misalignment without substantial wobble, but adds substantial expense to the component.
Double slider or "Oldham" couplings are known for coupling non-disengageable shafts. Wobble is reduced or eliminated by a center component sometimes called a "spider" having mating surfaces, channels or projections, on opposite ends which are rotated 90.degree. from each other. The mating surfaces of the spider mate with complementary surfaces on components fixed to the two shafts. Wobble is reduced or eliminated by continual radial sliding of the spider with respect to the two components fixed to the shafts. This particular coupling is not used as a disengageable coupling because the spider is held only by engagement with the other two members.